In many processing applications, e.g. for production of chemicals, foodstuffs and pharmaceutical compounds, containers or tanks are used for storing or processing various ingredients. These containers need to be cleaned from time to time. The need for cleaning may be controlled by many different factors, depending on industry and type of processing, e.g. to avoid cross contamination, adulteration and avoidable carryover, to prepare the container for processing of another batch, to remove or at least avoid build up of contamination layers such as bio-film, dried foam, precipitate or sediments, to comply with legal requirements, to prepare the container for human entry, to remove hazardous or explosive atmospheres, or to protect the processing equipment against corrosion or other degradation.
Such a need for internal cleaning of containers arises in all types of industries, including the fields of pharmaceutics, food processing, textiles, pulp and paper, paint, petrochemical processing, plastics, mining, etc. It is desirable to clean the containers as fast and efficient as possible, preferably without having to dismantle and clean the containers manually. There is also a general desire to reduce the consumption of water, chemicals and energy. To achieve one or more of these goals, so-called Cleaning-In-Place (CIP) systems have been developed. The CIP systems operate to supply a fluid inside the tank for cleaning purposes and may be either static or rotary.
A static CIP system may use a static spray ball inside the container to spray a chemical detergent onto the interior of the container, whereby the mechanical action of falling film acts to remove contaminations.
A rotary or dynamic CIP system may operate a rotary nozzle head to rotate slowly inside the container so as to generate and displace one or more fluid jets or sprays across the inner surfaces of the container, whereby the impact of the fluid at least partly acts to remove contaminations. In one type of rotary CIP system, the nozzle head is configured to generate confined liquid jets that are rotated both around a vertical axis in the container and a second axis with respect to the nozzle head, e.g. as disclosed in U.S. Pat. No. 5,333,630 and U.S. Pat. No. 5,715,852. Such a nozzle head is known as a “rotary jet head” (RJH) and operates to move the jet in mutually displaced loops on the inside the container, such that the loops collectively form a full pattern with desired coverage. In another type of rotary CIP system of simpler design, the nozzle head is configured to generate one or more sprays of fan-shaped flat type which are rotated around a vertical axis in the container, e.g. as disclosed in US2003/137895. Such a nozzle head is known as a “rotary spray head” (RSH).
Typically, CIP systems are highly automated, and there is a need to ensure proper cleaning of the container. For verification that the container is properly cleaned, the interior of the container may be physically inspected. This is however a labor intensive and expensive process.
A commercially available system for monitoring of an RJH CIP system is denoted “Rotacheck system” and provided by Alfa Laval. The Rotacheck system may be used for e.g. automatically estimating whether the interior of the container has been properly cleaned or not. The system includes a sensor which is installed in the roof of the container and has a small circular sensor diaphragm that generates a signal pulse when hit by a jet released by the rotary jet head. By evaluating the timing of signal pulses, the system is able to verify proper rotation of the rotary jet head. Since the RJH CIP system moves the jet slowly in mutually displaced loops, the time interval between signal pulses generated by the sensor for a particular jet may be significant, e.g. on the order of minutes, or even longer. Apart from causing an undesired delay in detecting e.g. malfunctions in the RJH CIP system, the long time interval between signal pulses causes an undesirable trade-off between response time and accuracy in detecting malfunctions. A fast response time may require a potential malfunction to be detected based on a single or a few signal pulses for a particular jet, resulting in a low accuracy and a risk for errors. The long time intervals also make the monitoring system vulnerable to interferences, e.g. caused by liquid splashes, measurement noise, and instabilities in the level of signal pulses, etc.
The prior art also comprises JP08-192125, which discloses a rotary CIP system that operates to rotate a spray ball around a vertical axis inside a tank, while the ball ejects a liquid through a series of holes to generate a 360° spray in a vertical plane. Poor rotation of the spray ball is detected based on signals from two spaced apart circular sensors arranged in the roof of the tank to measure pH, temperature or electric conductivity. This monitoring technique is sensitive to wetting of the sensors, splashes, etc.
JP2008-290003 discloses a rotary CIP system that comprises a rotary jet generation element which is suspended from the roof of a tank to generate a rotating jet of liquid. A conductivity sensor is suspended from the roof in parallel to the jet generation element so as to be intermittently hit by the rotating jet. A rotation failure may be detected by correlating the rotation of the jet generation element with the output signal of the conductivity sensor. This monitoring technique is sensitive to wetting of the sensor, splashes, etc. The use of a projecting sensor may limit the installation to certain types of tanks or applications, and may also lead to undesired accumulation of contaminations on the sensor itself.